The Rathdrum Aquifer: The Best of the Best!
No two aquifers are the same, and Spokane Valley-Rathdrum Prairie (sometimes abbreviated as SVRP) is particularly special. Covering 370 square miles and with approximate boundaries reaching Lake Pend Oreille, Lake Coeur d’Alene and Liberty Lake, the aquifer serves 600,000 people. The average person in the aquifer distribution area uses about 235 gallons per day, which puts us in the top 2% in the country for water consumption per person. Total water consumption from the aquifer is around 39 billion gallons per year. The top of the aquifer varies, reaching between 20 to 200 feet below ground level.
SVRP is uniquely prepared to provide the quantity of water needed by the people it serves. To understand how Rathdrum works, it’s important to note two major divisions in types of aquifers:
- Consolidated (where rocks hold groundwater)
- Unconsolidated (where sediments hold groundwater)
SVRP is considered an unconsolidated aquifer. This is good news because it means that water can flow in and out. This kind of aquifer acts like a filter instead of an underground lake, and everything eventually flows into Lake Spokane. Water flows through the aquifer at about 50 feet per day, instead of the more common 5 feet per day. When it comes to aquifers, this one is practically a Ferrari.
The Waterflow of an Unconsolidated Aquifer
Water entering the aquifer to replace the water lost through natural water flow and human use is called “recharge.” Aquifer recharge is lowest in the summer, and highest in the spring. Lots of different things fuel recharge, including:
- Precipitation
- Inflow from upland bedrock watersheds
- Seepage from lakes
- Seepage from Spokane River
- Water from irrigation
- Effluent from septic system
The aquifer hold approximately 3.2 trillion gallons of water, and recharges at about 237 billion gallons per day. That equates to about 11,000 gallons per second! In some areas, the Spokane River recharges the aquifer, and in others, the reverse. The river recharges the aquifer at Barker Rapid, and the aquifer recharges the river at Bowl and Pitcher.
Though recharge is lower in the warmer months, the aquifer did not run dry last summer. Avista reduced flow down the Spokane River to do maintenance at Post Falls dam.
Water Health and Access
There are 20 water purveyors in the district, and each one monitors its own wells. The aquifer is unconfined, meaning it has no protective layer above it to keep pollutants out. External natural barriers like grass swales help filter stormwater runoff. There are some 350 underground tank sites in the area, which catch stormwater runoff. Wastewater treatment plants can process up to 50 million gallons per day at the highest level of treatment available. In high risk areas, like around the railroad diesel storage facility in Hauser, there are test wells downstream to catch potential hazards before they become dangerous.
All these efforts Maintaining the health of aquifers is the responsibility of the Aquifer Board, but they have no power of enforcement. If the board encounters a violation in the health and safety of the aquifer, it is referred to the Department of Ecology, which is responsible for enforcement.